A doctor administers a measles vaccination to a 4-year-old as her mother holds her in this file photo taken at Miami Children's Hospital on Jan. 28, 2015. (Credit: Joe Raedle/Getty Images)

Gov. Jerry Brown on Tuesday signed into law one of the nation’s strictest childhood vaccination requirements, approving a bill that generated multiple protests and controversy as it moved through the Legislature.

Senate Bill 277, authored by Sacramento pediatrician state Sen. Richard Pan and former Santa Monica-Malibu school board president state Sen. Ben Allen, eliminates parents’ ability to claim “personal belief” exemptions to schoolchildren’s vaccine requirements at both private and public schools in California.

Only medical exemptions, approved by a doctor, will be allowed under the law. A licensed physician will have to write a letter explaining the child’s medical circumstances that make immunization unsafe for that child.

Children who are not vaccinated must be home-schooled or participate in public school independent study. The law goes into effect July 1, 2016.

The bill was approved by the Assembly on a 46-31 vote Thursday; the amended version was approved by the state Senate, 24-14, Monday.

Brown acknowledged in a signing statement Tuesday that the bill had generated controversy, saying both sides expressed “their positions with eloquence and sincerity.”

“The science is clear that vaccines dramatically protect children against a number of infectious and dangerous diseases,” Brown said. “While it’s true that no medical intervention is without risk, the evidence shows that immunization powerfully benefits and protects the community.”

State Sen. Dr. Richard Pan stands with supporters as he introduces a vaccine-related bill in Sacramento on Feb. 4, 2015. (Credit: KTXL)

Existing law allows unvaccinated children to attend school if their parents file a form claiming an exemption based personal beliefs — including religion. A law authored by Pan that went into effect in 2014 required that exemption-seeking parents talk to a health care provider about vaccination benefits and risks, or that they state their membership in a religion that prohibits them seeking medical care.

In fall of 2014, 2.54 percent of kindergarteners in California had personal belief exemptions on file, down from 3.15 percent the previous year, according to state data. Pan connected the drop in exemptions from 2013 to 2014 to the requirement that parents talk to licensed health care practitioner.

In 1998, only 0.77 percent of the state’s kindergarteners had a personal belief exemption, the Los Angeles Times reported.

The bill approved Tuesday by Brown was introduced after an outbreak of measles that began at Disneyland last year and sickened some 131 Californians. The legislation prompted protests by anti-vaccination parents, often clad in red.

Opponents of SB 277 rally in Sacramento. (Credit: KCRA via CNN)

Opponents include the group Californians for Vaccine Choice, whose members emphasize risks related to vaccination.

“The passage of any bill to repeal the personal belief exemption will create an even more hostile environment for California families who don’t agree with safety, efficacy, or necessity of every single dose of every single government mandated vaccine,” the group’s website states.

In a statement earlier this month, Dr. Pan said that the growth of opposition to vaccination was based in part on a now-retracted 1998 study that “falsified data to purport a link between autism and the measles vaccine.”

“Years of anti-science, anti-vaccine misinformation have taken its toll on immunization rates to the point that the public is now endanger,” Pan said in the statement.

Pan has emphasized “herd immunity” in many of his comments on the bill, saying that when immunization rates fall below 90 percent, those who cannot be vaccinated become at greater risk for infection, including infants and those with medical conditions that prevent them from being vaccinated.

A report from Los Angeles County Department of Public Health, released Tuesday, indicated that only 86 percent of the county’s kindergarteners were up to date with vaccinations in 2014, compared to 90 percent statewide.

The “West Service Planning Area” of the county — including largely wealthy areas such as Beverly Hills, Brentwood, Malibu, Pacific Palisades and Santa Monica — had the highest rate of personal belief exemptions, 6.4 percent, the report indicated.